Canadian environmentalists are calling for strict conservation measures as the controversial grizzly bear hunt begins over the Easter weekend in Canada's westernmost province.

A report by scientists at two environmental organisations said the kill rate in past seasons exceeded provincial limits and will endanger the animals considered a keystone species in the nation's ecosystems.

"The number of grizzlies being killed in British Columbia is excessive," Faisal Moola of the David Suzuki Foundation said in a statement.

"The government's own data show that humans are killing more grizzly bears than allowed, and the greatest cause of death is trophy hunting."

Figures of the existing bear population remain inexact, but the environmental report noted that even at best, it has now halved from an estimated 35,000 bears a century ago.

Part of the difficulty is that bears are solitary beasts, whose range extends over thousands of square kilometres.

Provincial figures have varied hugely, from an estimated 6,600 bears in the mid-1980s to about 16,000 cited in 2008.

The report called on British Columbia to stop trophy hunting of bears in parks and other protected zones, and to protect bears from all harmful human activities by setting up zones of inter-connected habitats for the furry beasts.

"In some cases, the number of grizzlies - which no longer exist or are at risk of extinction in parts of the world - killed by humans was more than double the number deemed allowable by the government," the Natural Resources Defence Council said.

The report, published by the Suzuki Foundation of Vancouver and the New York-based Natural Resources Defence Council, cited opinion polls that suggest a majority of provincial residents support a ban on hunting.